Air pollution increases the risk of acute cardiovascular events. Whether it contributes to the risk of hypertension and diabetes, chronic predisposing conditions to cardiovascular disease, is unknown. Hypertension and type 2 diabetes occur much more commonly among U.S. black women than white women, a discrepancy only partly explained by known risk factors. U.S. black women tend to live in neighborhoods with more air pollution than their white counterparts, regardless of socioeconomic status. With state-of-the-art methods, we propose to test the hypotheses that exposure to air pollution increases the risks of incident hypertension and type 2 diabetes in African American women. We will focus on particulate matter of d2.5 <g aerodynamic diameter (PM2.5) and traffic-related pollution as indicated by nitrogen dioxide (NO2) and oxide (NO). We will prospectively test the hypotheses in the Black Women's Health Study (BWHS), an ongoing cohort study of 59,000 U.S. black women. Detailed information on risk factors for disease, lifestyle factors, and disease endpoints was collected at baseline in 1995 and in biennial follow-up questionnaires. Preliminary findings based on Los Angeles participants indicate positive associations of the pollutants of interest with incident hypertension and diabetes, after control for personal and neighborhood socioeconomic status. We will estimate long-term exposure to PM2.5 concentrations based on a new U.S. data layer developed for Health Canada and provided to the study at no cost. We will use dispersion modeling to estimate traffic-related pollutants using the best indicators, NO and NO2. We will model traffic noise levels for the purpose of including noise as a potential confounder in the hypertension analyses. We will use the newly developed spatial cohort survival modeling technique to account for clustering of air pollutants at two geographic levels, regional and local. Exposure measures will be available for the entire BWHS cohort, which is geographically dispersed across the U.S. By the end of the 2007 follow-up cycle, 10,137 incident hypertension cases and 4861 incident type 2 diabetes cases had occurred in the BWHS, allowing for high statistical power. The BWHS cohort is particularly well suited to the study aims because it has high rates of hypertension and diabetes and high levels of exposure to air pollutants. The proposed study will be the first investigation of the effect of air pollution on incidence of hypertension, the first large-scale investigation its effect on incidence of diabetes, and the first study of air pollution effects specifically in African American women. The hypotheses are of critical public health importance, given the high and growing prevalence of hypertension and diabetes in the U.S., the disparity between incidence rates among U.S. black and white women, and the ubiquity of exposure to air pollution. Positive findings will inform public policy on air quality regulation, provide insight into a novel pathway whereby air pollution causes cardiovascular events, illuminate causes of racial disparities in hypertension and diabetes incidence, and spur research on effects of air pollutants on other diseases.